Multimedia has recently become popular, and a moving picture has been used more frequently. Image data has a large amount of information, and a moving picture, which is a sequence of images, has an amount of information corresponding to a bit rate of over 1 Gbit/sec with the Hi-Vision (1920×1080) broadcast which is a mainstream of TV broadcasts. A network environment, which is used for transmitting data of a moving picture, uses a band having a bit rate of 100 Mbit/sec at most even in optical services. Moreover, a bit rate in an effective band is on the order of 20 Mbit/sec, which is not large enough to transmit a moving picture as it is.
Furthermore, a maximum of seven minutes of Hi-Vision data may be recorded on a Blu-ray Disc, which is a typical storage medium, when the Blu-ray Disc has a dual structure for 50 GB. Accordingly, a compression encoding technique typified by H.264/AVC, for example, is used to compress the amount of information, and the compressed information is transmitted and stored.
H.264/AVC, a standard technique for encoding, uses tools, including an orthogonal transform, inter-frame prediction, intra-frame prediction, arithmetic encoding, and deblocking filtering, to achieve compression of a moving picture down to as small as about one-hundredth of the original size of the moving picture. A deblocking filter, which is one of the tools used in H.264/AVC, serves in such a manner that occurrence of block noise owing to encoding being performed on a macroblock basis is suppressed. A deblocking filter effectively suppresses degradation in image quality especially when a compression ratio is set to high.
Super Hi-Vision (7680×4320) technology, which has a resolution that is 16 times that of Hi-Vision, is currently being researched and developed actively. However, encoders and decoders that are compatible with Super Hi-Vision have not been developed. Consequently, Super Hi-Vision data is divided into pieces of data having a Hi-Vision size, which are individually subjected to a process using multiple encoders and decoders. With H.264/AVC, encoding is performed on a 16×16 macroblock basis. However, the size of a Hi-Vision image, 1920×1080, is not a multiple of sixteen. When a Hi-Vision image is to be encoded, the image is extended so as to become an image having a size of 1920×1088.
Typical methods for extending an image include a method in which a black or grey fixed pattern is added to the image, and a method in which an image portion at the edge of the image is extended. To suppress an adverse effect of an extension image on an original image (hereinafter, referred to as leakage of an extension image), which occurs when deblocking filtering is performed on the original image along with the extension image, the deblocking filter may be disabled when desired. Japanese National Publication of International Patent Application No. 2010-523054 describes deblocking filtering that achieves reductions in computational complexity and in memory access.